There are two kinds of frame structures in a Long Term Evolution (LTE) system. Frame structure type 1 is suitable for full-duplex and half-duplex Frequency Division Duplex (FDD). Each radio frame has a length of 10 ms and it is composed of 20 slots, each slot being 0.5 ms, and the slots are numbered from 0 to 19. One subframe is composed of two consecutive slots, for example, a subframe i is composed of two consecutive slots 2i and 2i+1. No matter whether the half-duplex FDD or the full-duplex FDD, uplink and downlink are transmitted in different frequencies, but for the half-duplex FDD, the UE can not transmit and receive data at the same time; and for the full-duplex FDD, there is no such limitation, i.e., there may be 10 downlink frames and 10 uplink frames within each 10 ms interval. As shown in FIG. 1, frame structure type 2 is suitable for the Time Division Duplex (TDD). One radio frame has a length of 10 ms, and it is composed of two half-frames with a length of 5 ms. One half-frame is composed of 5 subframes with a length of 1 ms. The supported uplink and downlink configurations are shown in Table one, wherein, in the table, “D” represents that the subframe is a downlink subframe, “U” represents that the subframe is an uplink subframe, and “S” represents that the subframe is a special subframe. The special subframe is composed of DwPTS, GP and UpPTS, with a total length of 1 ms. Each subframe i is composed of two slots 2i and 2i+1 with a length of 0.5 ms (15360×Ts), as shown in FIG. 2.
The frame structure Type 2 supports two uplink-downlink switching periods of 5 ms and 10 ms. In the 5 ms uplink-downlink switching period, both half-subframes have special subframes. In the 10 ms uplink-downlink switching period, only the first half-frame has a special subframe. Subframes 0 and 5 and the DwPTS are always reserved for the downlink transmission. The UpPTS and a subframe immediately following a special subframe are always reserved for the uplink transmission. Therefore, for the 5 ms uplink-downlink switching period, the UpPTS and subframes 2 and 7 are reserved for uplink transmission; and for the 10 ms uplink-downlink switching period, the UpPTS and subframe 2 are reserved for uplink transmission;
TABLE ONEUplink and downlink configurationsUplink Switching and downlinkperiod from aSubframe numberconfigurationsdownlink to an uplink012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
The following three downlink physical control channels are defined in the LTE: a Physical Control Format Indicator Channel (PCFICH); a Physical Hybrid Automatic Retransmission Request Indicator Channel (PHICH); and a Physical Downlink Control Channel (PDCCH).
Wherein, the information carried in the PCFICH is used to indicate the number of Orthogonal Frequency Division Multiplexing (OFDM) symbols for transmitting the PDCCH in one subframe, and it is transmitted in a first OFDM symbol of the subframe, and a frequency location where the information is located is determined by a system downlink bandwidth and a cell Identity (ID).
The PHICH is used to carry Acknowledgement/Negative Acknowledgement (ACK/NACK) feedback information of the uplink transmission data. The number of PHICHs and the time-frequency location can be determined by system information and a cell ID in a Physical Broadcast Channel (PBCH) of a downlink carrier where the PHICH is located.
The PDCCH is used to carry Downlink Control Information (DCI), including uplink PUSCH scheduling information, downlink PDSCH scheduling information and uplink transmission power control.
The DCI formats are divided into the following several types: DCI format 0, DCI format 1, DCI format 1A, DCI format 1B, DCI format 1C, DCI format 1D, DCI format 2, DCI format 2A, DCI format 3 and DCI format 3A and so on, wherein,
the DCI format 0 is used to indicate scheduling of a Physical Uplink Shared Channel (PUSCH for short);
DCI format 1, DCI format 1A, DCI format 1B, DCI format 1C, and DCI format 1D are used for different modes of one PDSCH codeword scheduling;
DCI format 2, DCI format 2A and DCI format 2B are used for different modes of spatial multiplexing;
DCI format 3 and DCI format 3A are used for different modes of Physical Uplink Control Channel (PUCCH for short) and power control signaling of PUSCH.